Magnetostrictive elements



Aug. 25, 1964 A. CLARK 3,146,380

MAGNETOSTRICTIVE ELEMENTS Filed Dec. 17, 1962 AA \/\/\AA \ZAA .0

C098765 ICr CHARLESAC RK INVEN ATTORNEY United States Patent 3,146,380MAGNETOSTRICTIVE ELEMENTS Charles Alfred Clark, Birmingham, England,assignor to The International Nickel Company, Inc., New York, N.Y., acorporation of Delaware Filed Dec. 17, 1962, Ser. No. 245,153

Claims priority, application Great Britain Mar. 13, 1959 1 Claim. (Cl.317-158) The present invention relates to magnetostrictive elements and,more particularly, to alloys for use in trans mitting magnetostrictivedevices operating at high frequency.

It is well known that magnetostrictive elements are used for theconversion of electrical to mechanical oscillations and vice versa, forexample, in transducers in echo-sounding apparatus and ultrasonicdrilling apparatus. A measure of the efliciency of the magnetostrictivedevice is given by the square of its electromechanical couplingcoefficient (K), which itself is a measure of the efiiciency of themagnetic material in converting magnetic to mechanical energy. Thedefinition of K is such that Converted mechanical stored energy Input.magnetic stored energy The coeflicient K may be determinedexperimentally and depends upon the material of the magnetostrictiveelement.

When the magnetostrictive element is used, for instance, in a transducerthat acts as a transmitter, it is not only the value of the coeflicientK that is important, but also that of a constant Q, which depends uponthe material used and in fact varies (when dilferent materials areemployed in magnetostrictive elements) inversely with the electrical andmagnetic losses which occur. Q is defined as Q: Electromagnetic storedenergy Electrical and magnetic energy losses It is in fact known thatthe product K Q should be as high as possible, particularly when thetransducer or other device containing the element is to operate at highfrequency. The value of the product K Q as exhibited by magnetostrictiveelements employed in transmitting devices is critical, since thesetransmitting devices utilize high levels of electrical input energy andconsequent high reactance resistance, impedance, etc., losses (e.g.,eddy currents, hysteresis, etc.). Although attempts were made to providea metallic magnetostrictive element having a high value of K Q, forexample, a value in excess of 1.1 when employed in the frequency rangeof about 25 to about 50 kilocycles per second (kc./s.), none, as far asI am aware, was entirely successful when carried into practicecommercially on an industrial scale.

It has now been discovered that by employing specially restricted rangesof alloying ingredients in an alloy comprising a magnetostrictiveelement, a very high value of the parameter K Q can be attained.

It is an object of the present invention to provide a novel alloy havingenhanced magnetostrictive characteristics.

Another object of the invention is to provide a novel magnetostrictiveelement having a high value for the K Q parameter.

The invention also contemplates providing a magnetostrictive devicehaving a high value for the K Q parameter when said device is employedat high frequencies.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in whichthe figure is a portion of a ternary diagram whereon the relation of thepercentage of nickel to the percentage of cobalt and to the per-3,146,380 Patented Aug. 25, 1964 "ice ' centage of chromium for thealloys of the present invention is depicted.

Generally speaking, the present invention contemplates amagnetostrictive element comprising a ternary nickelcobalt-chromiumalloy having a composition falling within the area bounded by the lineABCD in the part of the ternary diagram shown in the accompanyingdrawing. Substantially all these alloys have values of K Q, measured onspecimens 0.015 centimeter (cm.) thick, of 1.1 or more. Advantageously,the composition of the al loys is such that it falls within the areabounded by the line EFGH in the ternary diagram. Substantially all thealloys defined by this area have values of K Q measured on specimens0.015 cm. thick, of 1.3 or more. The invention further contemplates theuse of said alloys as magnetostrictive elements in the interconversionof electrical and mechanical oscillations comprising applying one ofsaid types of oscillations to the magnetostrictive element made of saidalloy and extracting the other of said types of oscillations therefrom.

Advantageous alloys in accordance with the present invention are setforth in the following Table I:

Table 1 Alloy No Percent Percent Percent 00 Cr Ni 1. 4 2. 3 Bal. 2. 0 1.3 Bal.

Table II Percent Percent Percent Point Or 00 Ni It has been found thatthe addition of chromium to a binary alloy containing nickel and up toabout 3.6% cobalt gives an enhanced value of K Q. No equivalentimprovement is found in alloys containing 8% or more cobalt.

In carrying the invention into practice, it is advantageous to employthe alloys in the form of thin sheets or plates having a thickness ofthe order of about 0.01 to about 0.04 cm. In making the alloys,commercially pure nickel is normally used, and, accordingly, the usualimpurities will also be present. Commercial nickel often contains smallquantities of cobalt and in making the alloys it is necessary to allowfor any cobalt present in the nickel.

Advantageously, the alloys are stamped into laminations and heat treatedfor one hour in dry hydrogen. The laminations are then insulated withvarnish and built up into a transducer stack of the required dimensions.When treated in this manner and tested by measurement of the electricalimpedance of the transducer as a function of Tgble 111,,

Ijncornparison, when tested under the identical conditions, prior art.alloyssuch as an alloycontaining 4% chromium and 96% nickelor analloy;containing .93% nicke1,,2% chromium. and"5% cobalt exhibit valuesfor. K of 0.25 and 0,35,; respectively, and values for the K Q parameterof'1'. 0. and 0'. 7, respectively- The respective values for thesecharacteristics clearlydemonstrate, as pointed out hereinbefore, thatthe alloys .andmagnetostrictive elements of the present invention canprovide more efficient trans,- mitters able; to operate at higherfrequencies than those having metallic magnetostrictive elements inaccordance with the prior art.

The present .invention is particularly applicable to transmittingtrans'ducers used on echo sounding and ultrasonic cleaning equipmentandultras'o'nic drills.

The present application'isacontinuation-in-part of my co-pcnding U.S.application, Serial No. 9,911, filed Febru ary 19, 1960, now abandoned.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within thepurview and scope of the invention and appended claim.

I claim:

A magnetostrictive element for use in transducing transrnitting devicesadapted to operate at high frequencies comprising a plurality ofthinelectrically insulated laminations' of an alloy consisting essentiallyof about 1.6% to about3% chromium, about 0.2% to about 2.3% cobalt, withthe balance being essentially nickel, said alloy being represented by apoint falling within the area EFGHE in the accompanying. drawing andsaidmagnetostrictive element being capable of exhibiting a highelectromechanical coupling coefficient and a value of K Q in excess ofabout l.3 when;subjected to a source of alternating energy.

ReferencesCited in the file of this patent UNITED STATES PATENTS1,882,396 Pierce Oct. 11, 1932 2,519,495 Nesbitt et al Aug 22, 1950ecu-main

